Fuse design for fire limiters or other safety appliances in ventilation installations

ABSTRACT

A fuse for safety appliances such as fire limiters in ventilation systems, the fuse comprising a first part, a second part, fusible material disposed between said first and second parts for normally maintaining said parts in fixed position with respect to one another when the fusible material is in solid form, a narrow path being defined for flow of fusible material in molten form, and the first and second parts being urged towards one another. The parts move towards one another when the fusible material melts and flows through the narrow path. The parts stop moving when the fusible material stops flowing with the parts again maintained in fixed position with respect to one another when the fusible material resolidifies.

BACKGROUND OF THE INVENTION

The present invention concerns a fuse design for tripping fire limitersor other safety appliances in ventilation installations, comprising afuse body part and a fuse material, the fuse material being disposed,when in solid state, to maintain the parts of the fuse in a certainposition relative to each other and when in liquid state, to permit theparts of the fuse to move with reference to each other.

It would be highly welcome in fire limiters if one fuse could be usedmore often than just once. It would be of importance that subsequent tofalse or test tripping for reasons other than fire, which occursfrequently in the case of fire limiters, the same fuse could beimmediately used for resetting. It is also important that theoperability of a fire limiter could be checked in a simple andconvenient manner regarding the structure other than the fuse, bytripping and resetting the closing member, e.g. the flap or louvre pack,once or several times. Convenient detachability and replaceability ofthe fuse are also advantages.

SUMMARY OF THE INVENTION

The currently most well known and most used design is a strip fuse, inthis structure two metal strips being soldered together with the aid offuse material having desired melting point. When the temperature of thefuse material rises to a pre-determined limit value, that is to themelting temperature, the strips become detached from each other. Adrawback of a structure of this kind is however that the same fusecannot be reused after false or test tripping. A strip fuse is alsoquite likely to suffer damage or to break. There is also the problem ofthe long-term strength of the fuse material and the difficult control ofthe soldering process.

Another fuse design known in the art is the so-called glass ball fuse inwhich between two latches are placed a glass ball filled with a liquidwith powerful thermal expansion, and which breaks when the liquidexpands. The set-up of the latches relative to each other is such thatwhen the glass ball bursts as the temperature reaches its given limitvalue they get free from each other. A drawback of this design is itssingle-use, expensive and inconvenient construction.

At present, reuse of the fuses proper is not possible, although it istrue that triggers based on thermal expansion are known in the art, forinstance a tripping mechanism wherein a stack assembled of bimetalstrips expands as it is heated and detaches a pin, connected to thestructure, from a locking hole, whereby tripping can take place. Adrawback of the structure has been found to be that the bimetal stripsreact slowly to temperature increase, and moreover the design isexpensive; it is rather susceptible to interference, easily damaged,sensitive to corrosion, and in case of fault awkward to repair.

The object of the present invention is to provide an improvement in fusedesigns known in the art. A more detailed object of the invention is toprovide a fuse design based on the melting of a substance and which isdurable, reliable in operation, resistant to corrosion, easy to test,favourable as to its manufacturing cost, easy to detach or replace, andwhich permits repeated use of the fuse.

In the German publicizing print No. 2 261 153 is disclosed a fuse designin which the fuse plate is subject to pressure. After the fuse materialhas melted, the molten substance flows off in uncontrolled manner, andtherefore reuse is not possible as a rule. In addition, the designrequires an ample amount of fuse material. The softening of the fusematerial at temperature below the melting point may also cause failureof the locking in this type of fuse because in it a harmful creep ispossible, which is a phenomenon typical of fuse materials.

The objects of the invention are attained with the aid of a fuse designwhich is mainly characterized in that the fuse material has beenarranged in molten state to flow through a narrow flow path arranged inthe fuse design under action of the internal pressure caused in the fusematerial by the locking forces acting on the fuse, for tripping the firelimiter or other safety appliance.

The fuse design according to an advantageous embodiment of the inventionis characterized in that after the internal pressure caused in the fusematerial by the locking force has dropped below the flowing limit, theflow of the fuse material ceases and the parts of the fuse cease to moverelative to each other, and that falling of the temperature below thesolidifying limit causes the fuse material to solidify so that the partsof the fuse will remain in this new position, thus enabling the firelimiter or other safety appliance to be reset with the aid of the samefuse one or more times.

By the fuse design of the invention, numerous significant advantages aregained, such as good durability, reliability in operation, resistance tocorrosion, favourable production costs, convenient testing, convenientdetachability, and replaceability. In the choice of material noattention need be paid to solderability either. In addition, no undueproblems are caused by the tripping of these fire limiters due to faultsor for testing, since they are so easy to reset.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail referring to certain advantageousembodiments of the invention presented in the figures of the drawingattached, but to which the invention is not meant to be exclusivelyconfined.

FIG. 1 presents an advantageous embodiment of the fuse design of theinvention in a schematic cross-section.

FIG. 2 presents another advantageous embodiment of the fuse design ofthe invention in a schematic cross-section.

FIG. 3 presents a third advantageous embodiment of the fuse design ofthe invention in a schematic cross-section.

FIG. 4 presents a fourth advantageous embodiment of the fuse design ofthe invention in a schematic cross-section.

FIG. 5 presents a fifth advantageous embodiment of the fuse design ofthe invention in a schematic cross-section.

FIG. 6 presents a fuse design as in FIG. 2, installed on a fire damper,in a schematic cross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fuse design depicted in FIG. 1 has been generally indicated by thereference numeral 10. The fuse 10 comprises a body part 11, in thepresent embodiment provided with a thinner tip portion 11a. On the endof the tip portion 11a of the body part 11 is disposed a sleeve-likemember 12, and between the tip part 11a and the sleeve-like member 12 isplaced the fuse material 13 which keeps the sleeve-like member 12 at acertain preselected axial distance with reference to the body part 11when the body part 11 and the sleeve-like member 12 tend under influenceof external force to move further into each other. In this embodiment,the sleeve-like member 12 is open at both ends. It is thus understoodthat the sleeve-like member 12 is joined by the fuse material 13 to thetip portion 11a of the body part 11. When the temperature rises, thefuse material 13 becomes liquid, and under effect of the axial force thesleeve-like member 12 is enabled to move in the direction of the bodypart 11.

The fuse design presented in the embodiment of FIG. 2 is generallyindicated by the reference numeral 20. In this embodiment, a sleeve-likemember 22 provided with a bottom 24 is disposed around the tip portion21a of the body part 21, and between the tip portion 21a and thesleeve-like member 22 is placed the fuse material 23, of which theviscosity in the course of temperature increase changes drastically atthe melting point and owing to the axial force fuse material 23 isenabled to flow into the free space between the tip portion 21a and thesleeve-like member 22, whereby the sleeve-like member 22 is enabled tomove in the direction of the body part 21. It is to be particularlynoted that at normal temperature the fluidity of the fuse material isvirtually nil, because of which no flowing of the fuse material willtake place even at extreme pressures, provided that clearance betweenthe tip portion 21a and the sleeve-like member 22 is appropriate inmagnitude.

The fuse design presented in FIG. 3 is generally indicated by thereference numeral 30. In this embodiment, too, about the tip portion 31aof the body part 31 has been disposed a sleeve-like member 32 having abottom 34.

The fuse material 33 is disposed between the tip portion 31a and thesleeve-like member 32. In this embodiment, the sleeve-like member 32 isprovided with a hole or passage 35, through which the controlled flow ofthe fuse material will take place.

Also in the embodiment of FIG. 4, there has been placed a sleeve-likemember 42 with bottom 44 around the tip portion 41a of the body part 41of the fuse design, generally indicated by the reference numeral 40, andthe fuse material 43 is disposed between the tip portion 41a and thesleeve-like member 42. The principle of operation of the permanent fuse40 is the same as that of the permanent fuse 30 shown in FIG. 3, withthe difference that in the embodiment of FIG. 4 the passage or hole 45has been made in the tip portion 41a of the body part 41. Consequently,in this embodiment the liquid fuse material has been arranged to flowinto a passage or hole 45 in the tip portion 41a.

The fuse design presented in FIG. 5 is generally indicated by thereference numeral 50. In this embodiment, too, on the tip portion 51a ofthe body part 51 is disposed a sleeve-like member 52 provided withbottom 54. A button of fuse material is placed between the tip portion51a and the sleeve-like member 52. In this embodiment, the fuse material53 is an annular fuse material button provided with an aperture 55, thatis, the fuse material button 53 itself has a hole or passage 55, intowhich the liquid fuse material has been arranged to move.

The operation of the fuse design 10,20,30,40 or 50 of the invention isas follows. When the fuse design 10 is connected to a fire limiter, acompressive force acts on the fuse material 13,23,33,43,53 over the bodypart 11,21,31,41,51 and the sleeve-like member 12,22,32,42,52, wherebythe movement of the sleeve-like member and of the body part11,21,31,41,51 of the fuse with reference to each other is preventedwhile the fuse material is in solid state. When the temperature rises tothe melting temperature of the fuse material 13,23,33,43,53, thefluidity of the fuse material begins to become considerably mobile andthe sleeve-like member will under influence of the force acting on thesleeve-like member be displaced with reference to the body part, wherebythe fire limiter is tripped.

In FIG. 6 is presented an advantageous practical application of the fusedesign of the invention. In this embodiment, the fuse 20 of FIG. 2 hasbeen installed on a fire damper, the shell of which has been indicatedby the reference numeral 26. To the shell 26 is attached a shapedcounterpiece 27 and a clamping arc 28 attached to the closing plate ofthe fire damper (not depicted) is clamped by the aid of the fuse and thecounterpiece 27 in the way that in the present embodiment the clampingarc 28 is impacted between the bottom 24 of the sleeve-like member 22 ofthe fuse and the counterpiece 27. The clamping may also be accomplishedwithout counterpiece 27, in which case the sleeve-like part 22 directlyclamps the clamping arc 28. The other end of the body part 21, threadedover a certain length, of the fuse 20 has been shaped as a screw head29, whereby it is simple to accomplish positive clamping of the clampingarc 28 by turning the body part 21. The body part 21 is encircled by abody part 21b provided with threads and attached to the shell 26.

When the temperature is low enough, the closing member can be set withthe aid of the fuse. The action of the fuse is based on changingviscosity of the fuse material and/or its ability to reattach when thetemperature has gone down. The body parts 21 and 21b are so dimensionedthat setting of the fire limiter cannot be accomplished without fusematerial.

The fuse can be used until the fuse material has run short in the spacebetween the body part and the sleeve-like member, or until the emptyspace 55 shown in FIG. 5 has been filled. Thereafter, a new fusematerial button can be inserted in the fuse or the entire fuse may bereplaced. By means of the fuse material quantity, the number of timesone fuse can be used may be regulated.

We claim:
 1. A fuse arrangement, comprisinga first part, a second part, said first part being constituted by a sleeve-like member disposed about said second part, and fusible material disposed between said first and second parts and normally maintaining said parts in fixed position with respect to one another when said fusible material is in solid form, a narrow path being defined in one of said first part, said second part, between said parts, or in said fusible material itself, for flow of said fusible material in molten form, and mens for urging said first and second parts towards one another, said urging means comprising a fire damper comprising an outer shell, said second part being secured into said outer shell, and a clamping arc abutting against said first sleeve-like member, whereby said parts are caused to move towards one another by said urging means when said fusible material melts and flows through said narrow path, said parts stop moving when said fusible material stops flowing, and said parts are again maintained in a new fixed position with respect to one another when said fusible material resolidifies and said fire damper being reclamped by tightening said second part in said shell after said fusible material has resolidified.
 2. The arrangement of claim 1, whereinsaid second part comprises a tip member extending into said sleeve-like member constituting said first part, and said narrow path being defined between said sleeve-like member and said tip member.
 3. The arrangement of claim 1, wherein said sleeve-member is open at both ends.
 4. The arrangement of claim 1, wherein said sleeve-like member is closed at one end and said sleeve-member is further provided with a channel therethrough constituting said narrow path.
 5. The arrangement of claim 1, wherein said sleeve-like member is closed at one end and said narrow path is disposed through said second part.
 6. The arrangement of claim 1, wherein said narrow path is disposed as an aperture within said fusible material.
 7. The arrangement of claim 1, wherein said second part is threaded and screwed into said outer shell.
 8. The arrangement of claim 1, additionally comprising a counterpiece attached to said shell and said clamping arc at opposite ends thereof.
 9. The arrangement of claim 9, wherein after depletion of said fusible material, said counterpiece and said clamping arc are situated such that said fire damper cannot be reclamped by tightening said second part.
 10. A fuse, comprisinga first part, a second part, fusible material disposed between said first and second parts and normally maintaining said parts in fixed position with respect to one another when said fusible material is in solid form, a narrow path being defined for flow of said fusible material in molten form, and means for urging said first and second parts towards each other, wherein said first part is constituted by a sleeve-like member disposed about said second part, said sleeve-like member being closed at one end and said narrow path being disposed through said second part, whereby said parts move towards one another when said fusible material melts and flows through said narrow path, said parts stop moving when said fusible material stops flowing, and said parts are again maintained in fixed position with respect to one another when said fusible material resolidifies.
 11. A fuse, comprisinga first part, a second part, fusible material disposed between said first and second parts and normally maintaining said parts in fixed position with respect to one another when said fusible material is in solid form, a narrow path being defined for flow of said fusible material in molten form, and means for urging said first and second parts towards each other, wherein said first part is constituted by a sleeve-like member disposed about said second part and said narrow path being disposed as an aperture within said fusible material, whereby said parts move towards one another when said fusible material melts and flows through said narrow path, said parts stop moving when said fusible material stops flowing, and said parts are again maintained in fixed position with respect to one another when said fusible material resolidifies. 